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API Publ 4693-2001 pdf free download

1. Lightweight components (low molecular weight) contain 1 to 10 carbon atoms (Ci to C10); evaporate and dissolve more readily than medium or heavy- weight components, and also leave fewer residual weather- ing compounds (often called residue) than medium or heavy- weight components; are thought to be more BIOAVAILABLE to animals (readily absorbed by an organism) than medium or heavyweight com- ponents; and are potentially flammable and readily inhaled, so, are of con- cem for human health and safety. Examples: Benzene, Toluene, Ethyl-benzene, Xylene, AL- KANES (see the first booklet in this series for more informa- tion). Because- lightweight components are biologically available to organisms and can be readily inhaled, their potential TOXIC- ITY to animals and humans is of concern. 0 2. Medium-weight components (medium molecular weight) contain 11 to 22 carbon atoms (Cil to C22); evaporate or dissolve more slowly, over several days, and may leave behind some residual weathering compounds which can appear as a coating or film; are sometimes regarded as more toxic than the lightweight components; and are not as bioavailable as lower-weight components, result- ing in lower chemical toxicity to animals. Example: POLY CY CLIC AROMATIC HYDROCARBONS (PAHs) (see the first booklet in this series for more information). 3. Heavyweight components (high molecular weight) contain 23 or more carbon atoms (2C23); undergo little to no evaporation or dissolution; can cause long-term affects via smothering or coating by re- sidual weathering compounds. These residuals may remain in the water column and sediments indefinitely (Helton, 1996); and are not very bioavailable, resulting in lower chemical toxic- ity to animals when compared to light or medium-weight components. Example: Asphaltenes (see the first booklet in this series for more information).
Crude oils are composed of various combinations of compounds in each or refined product’s tendency to remain in the environment for a long period of time follow- ing a discharge. Persistent oils are those crude andrefined oil products that may not be com- pletely removed from an af- fected environment as a result of weathering processes or cleanup operations. When reading persistence measure- ments, higher numbers mean greater persistence. Non-persistent oils and products will be rapidly ond completely removed from the affected environments through natural weathering processes. They are largely composed of light-weight components. Only short-term effects are ex- pected from non-persistent oils. Pour point is the tempera- ture above which an oil begins to flow. of the three component categories. When comparing crude oils, the concentration of the larger molecular-weight compounds (medium and heavyweight) relative to the amount of lightweight components within the oil affects PERSISTENCE. Oils with greater concentrations of me- dium and heavyweight components will typically have greater persis- tence. Because oils with greater persistence remain in the environment longer, they lengthen the period of time during which organisms are at risk of exposure. Oils composed primarily of the lightweight compo- nents are usually considered NON-PERSISTENT. For purposes of illustration, Table 1 lists some of the differences in com- mon petroleum products. For more information on this topic, a full dis- cussion of the properties of different oil types can be found in the first booklet, “Fate of Spilled Oil in Marine Waters: Where Does It Go? What Does It Do? How Do Dispersants Affect It?: An Information Booklet for Decision-Makers .”
The effects of oil depend on the chemical composition of the oil itself. To be harmful, oil components must be bioavailable to the organisms. Some components which are considered harmful (i.e., alkanes in the C1 to C10 range) have a high volatility. This means that, unless the concen- tration of oil is very high, they will usually evaporate before becoming bioavailable to organisms in the water column. Other oil components are also considered harmful, but their molecules are very large, making them less soluble in water.

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